This report describes the functions of point of sales systems and the specific areas of risk to tax administrations. It sets out in detail the electronic sales suppression techniques that have been uncovered, in particular “Phantomware” and “Zappers”, and shows how such methods can be detected by tax auditors and investigators. The report also considers a number of strategies adopted in different countries to tackle electronic sales suppression and highlights best practices. In particular, it makes a number of recommendations to countries for addressing this important area of risk.